As I understand it, then I have to create Sample.cpp which describe the method jni_onload (), getmethodid (), getsum ();

Further difficulties arise (:

In the example in the method SimpleAudioEngineJni.cpp getmethodid () is a line:
classOfCocos2dxActivity = env-> FindClass (“org/cocos2dx/lib/Cocos2dxActivity”);
I describe my class? or in the class Cocos2dxActivity describe all methods of class Sample?!